The average American city during the 19th century was a breeding ground for the frequent epidemics that occurred, killing thousands. Port cities were particularly susceptible to epidemics of infectious disease. New York, Boston, and Philadelphia were places where ships carrying foreign goods-and disease- were unloaded; they were also where potentially infected immigrants disembarked.
Toward the end of the 19th century, as people searched for a way to control infectious diseases, the germ theory of disease was introduced. It became clear that impure water, crowding, poor housing, spoiled food, and other environmental conditions were contributing to high rates of disease in cities. In New York City, one out of every 36 people died in 1863, as compared to one out of 44 in Boston and Philadelphia. 190 infants out of every 1,000 didn't live to their first birthday, while nearly one-quarter of those reaching the age of 20 would not live to see thirty from 1840-1870.
Which diseases affected 19th century populations the most? Cholera, yellow fever, and influenza, malaria, TB, and smallpox had the most major epidemics in the United States during the 1800's. Influenza, a common respiratory ailment transferred by aerosol droplets, occurred (continues to occur) in world-wide epidemics,